A method for a friction facing material and carrier assembly

ABSTRACT

A friction facing material and carrier assembly (2) to form a part of a driven plate of a friction clutch. The assembly (2) comprises a circular carrier plate (4) with resilient flexible paddles (14) at its periphery. Two annuli of friction material constituting friction facings (20,22) are each bonded by silicone rubber to opposite sides of the paddles. The silicon rubber on each side of the paddles is in the form of substantially continuous circular concentric strips of rubber substantially centered on axis (X) about which the assembly (2) is intended to rotate. The concentric strips (24A, 24B, 24C, 24D, 24E), bonding the friction facing (20) to one side of the paddles (14), are each preferably opposite the gap between two adjacent concentric stripes of rubber bonding the friction facing (22) to the other side of the paddles.

This invention relates a friction facing material and carrier assemblyfor a clutch driven plate.

The driven plate may be used in a dry friction clutch.

In particular, though not exclusively, the clutch driven plate may beused in a clutch for a motor vehicle.

The friction facing and carrier assembly concerned is of a type(hereinafter called "the type referred to") comprising at least oneannular array of friction material adhered to a carrier by elastomericmaterial, and in use said assembly being intended for rotation about aaxis.

U.S. Pat. No. 4,529,079 discloses an assembly of the type referred to inwhich two continuous rings of friction material are adhered to oppositesides of a substrate, each ring of friction material being bonded to arespective side of the substrate by a plurality of small, discrete wellspaced regions of elastomeric material in the form of dots or roundblobs, or as rectilinear stripes extending radially of the ring offriction material, or as a combination of radial stripes and shortrectilinear stripes extending tangentially of the ring. A drawback withthe blobs and radial stripes in that, when the assembly is in use andtorque is input thereto to rotate the assembly, the rotary force actingin shear on the regions of elastomer can peel or roll off each region ofelastomer (starting initially at the trailing side of each region) fromthe facing material or the substrate thus weakening and possiblyeventually destroying the bond between the substrate and the facingmaterial. The same thing can happen when the regions of elastomer are acombination of the radial and short, rectilinear, tangential stripes asaforesaid.

An object of the invention is to provide an assembly of the typereferred to in which said drawback is avoided or at least mitigated.

According to one aspect of the present invention a friction facing andcarrier assembly of the type referred to is characterized in that saidcarrier is formed with one or more voids therethrough each spanned bysaid annular array of friction material and said annular array offriction material is bonded to said carrier by a plurality of stripes ofsaid elastomeric material, each said stripe extending around said axisin continuous contact with the array of friction material, and radiallyof said axis said stripes being at least mainly spaced one from another.

According to a further aspect of the present invention a friction facingand carrier assembly of the type referred to is made by a methodcharacterized in that an elastomeric material is applied to at least onearray of friction material in the form of a plurality of stripes, eachsaid stripe extending around said axis in continuous contact with thearray of friction material, and radially of said axis said stripes beingat least mainly spaced one from another, and said stripes are appliedagainst a carrier which is formed with one or more voids such that eachsaid void is spanned by said annular array of friction material, so asto adhere said array to said carrier.

By making the bonding stripes of elastomer substantially continuous, theregion or each of the regions of elastomer constituting a said stripe isrelatively long and tends not to be small. This increases the shearresistance in each region and thus provides enhanced resistance to bondfailure.

Each said stripe may be a substantially circular stripe.

The circular stripes may be disposed as substantially concentric circleslying in a substantially common plane, said circles having substantiallythe same centre lying substantially on said axis.

In a preferred embodiment each said stripe is completely continuous.

Preferably at least one passage is provided which allows flow of gasinto and out of a space between two adjacent said stripes of elastomericmaterial. During curing or vulcanising of the elastomeric material whichcauses the friction material to become bonded to the carrier, then eachpassage permits exposure (in said space) of the two stripes of elastomerto the ambient atmosphere which may be heated and/or comprise a mixtureof gases and vapours intended to promote said curing, and, veryimportantly, the or each passage can allow the escape of gases emittedby the elastomeric material during the course of curing.

Although a porous, or microporous elastomer might be used, preferablythe elastomer in an homogenous solid.

The elastomer may be a silcone rubber which vulcanises at roomtemperature so that distortion by vulcanization heating may be avoided.

The elastomer may have the following physical specification:

    ______________________________________                                        Durometer shore A Hardness                                                                        45                                                        Tensile strength    28.12 Kg/cm.sup.2 (400 psi)                               Elongation          300%                                                      ______________________________________                                    

The invention will now be further described by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a plan view of a fragment of an embodiment of a frictionmaterial and carrier assembly formed according to the invention andintended to form a part of a dry friction clutch driven plate;

FIG. 2 is a section of line II--II in FIG. 1;

FIG. 3 is a section, on an enlarged scale, on line III--III in FIG. 1;

FIG. 4 is a section, on an enlarged scale, on line IV-IV in FIG. 1;

FIG. 5 is a fragment, on an enlarged scale, of a friction facing in thecourse of a method of making the assembly in FIG. 1;

FIG. 6 is a plan view of a friction facing with another array of stripesof elastomer to be used in a second embodiment of friction material andcarrier assembly intended to form part of a dry friction clutch drivenplate;

FIG. 7 is a section comparable to FIG. 2 but of the second embodiment;

FIG. 8 is a section comparable to FIG. 3 but of the second embodiment,and

FIG. 9 is a section of the second embodiment, similar to FIGS. 7 and 8,but at an interruption in the stripes of elastomeric material.

In the drawings like or comparable parts have the same referencenumerals.

With reference to FIGS. 1 to 5 of the drawings a friction material andcarrier plate assembly is shown at 2 intended to form part of a frictionclutch driven plate which can be used in a clutch, for example, adiaphragm spring clutch which may be used, for example in a motorvehicle.

The assembly comprises a mainly flat steel carrier plate 4 of disc formcentrally apertured at 6 to fit, for example, on an internally splinedhub (not shown) known per se when the assembly is incorporated in a saiddriven plate. Aperture 6 is surrounded by a flared or Bellevillemarginal portion 8. Also the carrier plate is formed with windows 10 fortorsional vibration damping springs (not shown) known per se and holes12 for stop rivets (not shown) know per se.

At its periphery the carrier plate 4 has a plurality of outwardlyprojecting paddles or spokes 14 integral with the main body of thecarrier plate. The spokes are flat being substantially co-planar withthe main body of the carrier plate and are substantially equi-angularlyspaced about a central axis X about which the assembly 2 is intended torotate in use. Voids in the form of slots 16 space the spokes which havesubstantially radial opposite edges 18.

In the example shown there are thirty spokes 14 and thirty slots 16.Circumferentially each spoke 14 extends over about 7° of arc and eachslot 16 over about 5°. If desired the number, size, shape and spacing ofthe spokes can be varied.

The spokes 14 are axially pliable in the sense of being leaf springscapable of flexing resiliently along directions substantially paralledto the axis X. This enables the carrier plate 4 at the spokes 14 to besinuously flexible circumferentially.

Two substantially coincident and co-axial annular friction facings 20and 22 are respectively bonded by an elastomeric material 24 to theopposite faces of each spoke 14. The elastomeric material 24 is adhereddirectly to faces of the friction facings 20, 22 and of the spokes 14.The elastomeric material is preferably a heat resistant synthetic rubberfor example a silicone rubber. The rubber can be a room temperaturevulcanising (called RTV) rubber. An example of such a silicone rubber isRTV 7057 produced and sold by Dow Corning. Another example is ELASTOSIL(Trade Mark) E14 produced by Waker-Chemi G.m.b.H, and a further exampleis RTV 159 produced by General Electric Company of the U.S.A. However asilicone rubber of the fluoro-silicone rubber kind may also be used.

Desirably the rubber is of a kind which can withstand temperaturesexperienced by friction facings in use without the rubber degrading toloose its necessary bond strength or resilience. It is believed that therubber should be able to withstand temperatures from approximately -30°C. up to about 250° C., but an ability to withstand higher temperaturesis thought desirable, for example up to about 300° C. or higher.

The eleastomeric material is applied in discrete, radially spacedamounts as continuous, concentric annular stripes or beads havingsubstantially the same centre on the axis X. As can be seen more clearlyin FIGS. 3 and 4 the circular stripes or beads A, 24B, 24C, 24D, 24Ebonding the friction facing 22 to the paddles are opposite the spacesbetween the circular stripes or beads 24F, 24G, 24H, 24J, 24K, 24L, ofthe elastomeric material bonding the friction facing 20 to the paddles.

Each friction facing 20, 22 can be formed of any suitable frictionmaterial and may be of a non-asbestos type, but the facings are somewhatresilient such that each facing can flex or deform at leastcircumferentially

The facings 20 and 22 may each be thin, for example 2.00 mm or less inaxiall thickness. However the friction facings may be thicker than 2.00mm.

Due to the sinuous flexibility of the carrier plate 4 and the resilientand flexible nature of the friction facings 20 and 22, the whole of thefriction facings and carrier plate assembly 2 is sinuously flexiblecircumferentially at the spokes 14.

The layers of elastomer 24 provide resilient cushioning between thefriction facings and the paddles 14 and an overall axial cushioningbetween the friction facings. The layers 24 can each be of anappreciable thickness so that that coupled with adequate flexibilityand/or resilience of the friction facings will allow an appreciablelocal compression or axial compliance of the sandwich comprising bothfriction facings and elastomeric layers under an axial pressure appliedto a relatively small area of each friction facing at any region of thewhole area of the facing.

However when the assembly 2 forms part of a clutch driven plate in usein a motor vehicle clutch such as a diaphragm spring clutch, thesubjective feel and quality of clutch re-engagements may be furtherenhanced by provision of further cushioning such as between the pressureplate and diaphragm spring and/or between the diaphragm spring and aclutch cover. That further cushioning may be a wavy wire fulcrum ring asin British Patent No. 1583403.

Since the elastomeric bonding material 24 is to be used in a clutchdriven plate it has to have both the aforesaid resistence to degradationby heat and also have good shear strength in both the mass of theelastomeric material and in the bonds it forms between itself and thefriction facings and paddles.

To manufacture a friction material and carrier plate assembly which isin accordance with the invention, the elastomeric material in a fluid orpaste form can be sandwiched between the carrier plate and frictionfacings and whole subject to some axial pressure to ensure good areacontact between the elastomeric material and respectively the carrierplate and friction facings, but preferably the friction facings aremaintained a pre-determined distance apart. For example removeablespacing means can be disposed between the carrier plate and frictionfacings to ensure the elastomeric material layer between the plate and arespective friction facing has at least a minimum desired thickness.Then the elastomeric material is cured or vulcanized to render it solidand the spacing means are thereafter removed.

As shown in FIG. 5, during manufacture of the assembly 2 (FIG. 1) theelastomeric material is applied as a paste in the form of circularstripes, for example by a combing or extruding method, to each frictionfacing. Then the stripes on the facings are applied against the paddles14 and vulcanized. In the case of an RTV rubber vulcanising is merely bysubjecting the paste to the appropriate room temperature and humidityfor sufficient time. For example RTV 7057 vulcanises in aboutforty-eight hours at a temperature of about 25° and about 50% humidity

As shown in FIGS. 3 and 4 the elastomeric stripes attached to eachfriction facing do not extend through the slots 16 to the other frictionfacing, leaving at the slots 16 generally radially extending passages(such a passage being indicated in FIG. 4 by the double headed arrowsa). Those passages allow gases, emitted by elastomeric stripes duringcuring of the elastomer, to escape. The passages also allow the ambientatmosphere to have full access to both complete opposite sides of eachcircular stripe of elastomeric material.

The stripes of elastomeric material in the embodiment in FIGS. 1 to 5are in the form of continuous concentric circles. Instead of beingsubstantially true circles each stripe may have some other formdescribing a closed figure, for example each stripe may have a wavy orsinuous or zig-zag form. Also the stripes may touch one anotherperiodically.

The use of substantially concentric stripes of elastomer facilitates theassembly method and reduces the time in which the stripes are applied tothe friction facings because each facing need merely be rotated about anaxis to which a row of an appropriate number of elastomer extrusionnozzles is substantially radial. Thus the facing is quickly ready forapplication to the carrier plate and this reduces the chance ofsufficient time elapsing which would allow a skin to form on theelastomer before the facing :,s applied to the carrier plate. This is anadvantage because the formation of skin on the elastomer stripes beforethey are stuck to the carrier plate can reduce the shear strength of theelastomer bonds. Therefore when substantially concentric stripes ofelastomer are used, the technique optimises the shear strength andallows a fast method of assembly to be used without skinning.

Instead of being completely continuous at least one of the stripes mayhave at least one interruption therein. The or each interruptionsubtends at axis X an angle of only a few degrees whereas any intactlength of the stripe subtends at said axis an angle at least severaltimes more than a few degrees, and where the stripe has a plurality ofsuch interruptions the total agregate of the angles subtended by theinterruptions does not exceed about 60°.

If desired, the carrier plate 4 may have an annular circumferentialrim-portion 26 indicated in part in dotted lines with which the paddles14 are integral so that the voids 16 are wholly surrounded by thematerial of the carrier plate 4.

In the embodiment shown in FIGS. 6 to 9, 2' indicates an alterntivefriction facing and carrier assembly in which the friction facing 22 inbonded to the paddles 14 by concentric circular stripes of elastomericmaterial 24A, 24B, 24C, 24D and 24E which have short interruptions 28therein. At the axis X each interruption 28 subtends an angle b, andeach intact length of each stripe of elastomer subtends at angle c atthe axis X. Angle b is only a few degrees, in this example about 5° andis substantially equal to the circumferential angular span of each slot16. Angle c is several times greater than b, in this example angle c issubstantially 85°. In this example the aggregate value of the angles bdoes does not exceed about 20°.

The friction facing 20 has a array of concentric stripes of elastomer224A, 224B, 224C, 224D and 224E similar to that in the facing 22. Thusas shown in FIGS. 7 to 9 each stripe of elastomer on one friction facingis substantially opposite a said stripe of elastomer on the otherfriction facing so that at most voids or slots 16 the stripes ofelastomer on the facing 20 unite with the corresponding stripes ofelastomer on the facing 22 as shown in FIG. 8. However the interruptions28 in the elastomer on one friction facing are opposite theinterruptions in the elastomer on the other facing and coincide withcertain ones of the slots 16 as shown in FIG. 9. Thus in the assembly 2'four substantially radial passages exist (one indicated in FIG. 9 bydouble headed arrow d) for the free passage of gases between the ambientatmosphere and the arcuate chambers between adjacent stripes ofelastomer on each friction facing. In a modification at least one stripeof elastomer on one friction facing can be opposite a space between twoadjacent stripes of elastomer on the other facing.

A said interruption 28 in a said stripe of elastomer need not coincideradially with an interruption in another elastomer stripe. Instead, infirst and second radially adjacent stripes an interruption (theinitially mentioned interruption) in the first stripe can be off-set orstaggered circumferentially from an interruption (the latterly mentionedinterruption) in the second stripe wherein of any interruptions in thesecond stripe said latterly mentioned interruption is the more adjacentcircumferentially to the initially mentioned interruption. But if theelastomer stripes on one friction facing are opposite the elastomerstripes on the other facing, then at least one interruption in aradially innermost or outermost stripe should coincide with a said void16.

I claim:
 1. A method of forming a bonded friction facing material andcarrier assembly for a clutch driven plate rotatable about an axis, theassembly comprising a carrier formed so as to define at least one void,at least one array of friction material, and elastomeric material, themethod comprising the steps of:applying the elastomeric material to saidone array of friction material in the form of a plurality of stripessuch that each said stripe extends around said axis in continuouscontact with said one array of friction material, and radially of saidaxis, said stripes being at least mainly spaced one from another; andapplying said stripes against the carrier such that said at least onevoid is spanned by said one array of friction material, so as to adheresaid one array of friction material to said carrier.
 2. A methodaccording to claim 1 wherein each said stripe is completely continuous.3. A method according to claim 1 wherein the carrier has opposite sideand the elastomeric material is applied to the two annular arrays offriction material and each is adhered to a respective opposite side ofthe carrier.
 4. A method according to claim 1 wherein each said stripeis substantially circular.
 5. A method according to claim 4 wherein thestripes are disposed as substantially concentric circles lying in asubstantially common plane, said circles having substantially the samecentre lying substantially on said axis.
 6. A method according to claim1 wherein the elastomeric material is applied as a paste.
 7. A methodaccording claim 6 wherein said stripes are formed by combing.
 8. Amethod according to claim 6 wherein said stripes are formed byextruding.
 9. A method as claimed in claim 8 wherein at least one ofsaid stripes is formed with at least one interruption therein.
 10. Amethod as claimed in claim 8 wherein the stripes of elastomeric materialare concentric with one another and applied to said one array offriction material by a row of extrusion nozzles, each stripe beingapplied by a respective nozzle.
 11. A method as claimed in claim 10wherein said one array of friction material is rotated about its axis asthe elastomeric material is extruded through the nozzles.